The field of the invention is processes for making porous ceramic composites and their use in forming ultrafilters and catalyst supports.
Porous ceramic composites have been used to form ultrafilters and catalyst supports. The ultrafilters separate gases, liquids and particles. The catalyst supports are used for gas and liquid phase reactions.
The porous ceramic material must have a high ratio of surface area to mass and a a high flow rate for a filtered fluid. The high ratio of surface area to mass is achieved through either a thin layer of a ceramic composite having fine interconnected pores. The high flow rate is achieved through a substrate of a ceramic composite having interconnected course pores. The thin layer of a fine porous composite is deposited on top of the courseporous substrate. A high flow rate is achieved by making a fine pore membrane as thin as possible and by applying a high pressure across the membrane.
In a process using a catalyst the catalyst support is formed out a ceramic composite having course pores and fine pores. The catalyst support should be chemically and physcially stable. This requirement of physical and chemical stability makes porous ceramic composites desirable as a catalyst support. The fine pores provide a high ratio of surface area to mass in order to maximize both the contact and the interaction between a fluid, either a gas or a liquid, and the catalyst, such as particles of platinum. The course pores permit the fluid to flow through the catalyst support at a high flow rate.
U.S. Pat. No. 4,981,590 teaches a microfilter which includes a support layer which is formed out of a ceramic composite having course pores and a thin layer which is formed out of a ceramic composite having course pores. The support layer and the thin layer are firmly bound to each other. There is a sharp geometric transition between the support layer and the thin layer. If the thin layer has any pin-holes then the microfilter is ruined.
U.S. Pat. No. 4,689,150 teaches a separation membrane which includes a glassy microporous porous support. The separation membrane has excellent heat resistance, corrosion resistance, durability, gas-separability and high mechanical strength. The separation membrane is preferably provided with a metallic or ceramic microporous membrane vapor-deposited on the surface of the glassy microporous membrane. The separation membrane can be utilized with high efficiency in such diversified fields as either microfiltration or ultrafiltration of fluids, either gases or liquids.
U.S. Pat. No. 4,562,021 teaches a microfilter which includes a support layer of a ceramic composite having interconnected course pores and a thin layer of a ceramic composite having interconnected fine pores. Hydrolysis is performed on an alkoxide, an organo-metallic compound in order to obtain a sol of particles of the oxide. A thickening agent is added to the sol. The resulting sol is slip casted to form the thin layer which is deposited onto the support layer. The thin layer deposited on the support layer is then dried and heat treated to eliminate the thickening agent and to sinter the particles of the deposited thin layer. In Chapter 14, entitled "Ultrafilters by the Sol-Gel Process," of Ultrastructure Processing of Advanced Ceramics, published by John Wiley & Sons of New York in 1988, Louis Cot, Andre Larbot amd Christian Guizard have discussed the use of membranes in operations requiring separation.
U.S. Pat. No. 4,874,516 teaches a microfilter which includes a support layer of a ceramic composite having interconnected course pores and being of a high strength. The support layer is covered by and supports a microporous membrane of a polymer, such as a fluorocarbon polymer, which partly permeates the surface of the support layer and which acts as a microfilter for fine particles. The microfilter exhibits excellent corrosion-resistance, durableness and heat-resistance.
U.S. Pat. No. 4,581,126 teaches a catalyst support which includes a porous gel of an inorganic substance, for example a refractory inorganic oxide, and has a surface area in the range 125 to 150 square meters per gram, a mean pore diameter in the range of 140 to 190 angstroms with at least 80% of the pore volume contained in pores having a pore size range of 50 to 90 angstroms.
U.S. Pat. No. 4,969,990 teaches a catalyst which is useful for hydroprocessing a hydrocarbon-containing oil and which contains at least one hydrogenation component on an amorphous, porous refractory oxide. The catalyst is prepared by impregnating support particles having a narrow pore size distribution and a mode pore diameter from about 70 to 80 angstroms with a solution containing a precursor of the hydrogenation components, followed by drying and calcining. The catalyst is useful for promoting a number of hydrocarbon hydroprocessing reactions, hydrogenative desulfurization, demetallization and denitrogenation, and hydrodesulfurization of residuum-containing oils.